1. Field of the Invention
The present invention relates to a broadcast/multicast service (referred to hereinafter as ‘BCAST service’) and, more particularly, to a BCAST service system for transmitting broadcast contents to terminals when a network load is small, and its contents transmission method.
2. Description of the Related Art
Broadcast services provided in a mobile communication system include a broadcast service that transmits contents of a program to terminals ahead of an actual broadcast time if the broadcast service is not a live broadcast.
When the broadcast service is in use, a network operator transmits contents when a network usage rate is low, whereby network resources can be effectively used, a user can seamlessly receive a service without delay, and a loss of battery power can be minimized. For example, the terminals can receive the contents in real time during a sleep mode, and when the transmission is completed, the terminals are changed to a long sleep mode to reduce unnecessary power consumption.
Accordingly, the broadcast service has advantages in that a contents of a program (e.g., a program guide) can be received before an actual broadcast time and the received contents can be received such that the user can know when an actual broadcast will be provided. An OMA BCAST defines this service concept as a distribution window (DW) and a presentation window (PW).
FIG. 1 shows the concept of the DW and PW.
With reference to FIG. 1, the DW is a unit of time during which contents of a certain program are transmitted to the terminals ahead of an actual broadcast time. The DW is divided into a distribution start time and a distribution end time. the PW is a unit of time for designating the contents received during the DW according to an actual broadcast time to allow the user to watch the contents. The PW is divided into a presentation start time and a presentation end time. Namely, the PW refers to a time interval during which the user can watch the program contents in an actual broadcast time, and the DW refers to a time interval during which the related contents are broadcast in advance to allow the user can to select and view the program contents during the PW.
In order to transmit the contents during the DW, a server attempts to connect with the terminals by turning a control signal on or off (e.g., sending or not sending a signal) to wake up the terminals so as to receive the contents. This involves an exchanging of contents between the network and the terminals, and the user can note the time periods of the DW and the PW by viewing a service guide provided to the user.
FIG. 2 shows an example of a service guide employing the DW and the PW.
With reference to FIG. 2, in the left schedule table, the Content ID indicates the title of a program to be aired during a particular time, and the Presentation Window (PW) indicates a time interval during which an actual program is played. The Distribution Window (DW) is established ahead of the PW, the actual broadcast time. As a result, by transmitting the contents of the program to the terminals during the DW ahead of time, the users may receive and watch the contents in an improved manner.
However, in the related art broadcast service using the DW and the PW, if s the terminal is located in an OFF state or located in a shadow area (i.e., a poor coverage area), if memory capacity of the terminal is not sufficient, and/or if battery capacity of the terminal is not sufficient, the terminal may fail to receive the contents during the DW. Also, the server cannot check whether all terminals have properly received the contents during the DW and the users cannot watch a normal program during the PW because of service delays or discontinuation.